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Ability of Different d-Dimer Tests To Exclude Deep Venous Thrombosis and Pulmonary EmbolismFREE

The summary below is from the full report titled “d-Dimer for the Exclusion of Acute Venous Thrombosis and Pulmonary Embolism. A Systematic Review.” It is in the 20 April 2004 issue of Annals of Internal Medicine (volume 140, pages 589-602). The authors are P.D. Stein, R.D. Hull, K.C. Patel, R.E. Olson, W.A. Ghali, R. Brant, R.K. Biel, V. Bharadia, and N.K. Kalra.

What is the problem and what is known about it so far?

Deep venous thrombosis (DVT) is the formation of a blood clot in the deep veins of the legs. Pieces of the clot can break off and travel through the bloodstream to the lungs. Pieces that end up clogging arteries in the lungs cause a condition called pulmonary embolism (PE). DVT and PE can cause serious symptoms and even death if they are not diagnosed and treated quickly. Doctors may use one of several standard tests to diagnose DVT. These include an x-ray taken after injection of a liquid dye into a vein (venogram) or a scan that uses sound waves to look at blood flow in the veins (compression ultrasonography). To diagnose PE, doctors may use an x-ray taken after injection of dye into an artery in the lung (pulmonary angiography) or a scan that measures the amount of air (ventilation) and blood flow (perfusion) in the lungs (V/Q scan). To help diagnose DVT and PE, doctors also could use blood tests (d-dimer tests) that help measure whether a clot has formed and is breaking down. However, d-dimer can be measured in several different ways, and doctors may not know which d-dimer test is best.

Why did the researchers do this particular study?

To determine whether certain d-dimer blood tests are better than others for diagnosing DVT and PE.

Who was studied?

Patients with suspected DVT or PE who received a d-dimer blood test and also had standard tests for DVT or PE.

How was the study done?

Rather than doing a new study, the researchers searched the medical literature from January 1983 through January 2003. They found 78 studies that involved patients with suspected DVT or PE who had a d-dimer blood test. d-Dimer tests that were studied included enzyme-linked immunosorbent assays (ELISA), quantitative latex agglutination assays, semi-quantitative agglutination assays, and whole-blood agglutination assays. All of the patients in the studies also had standard tests for DVT or PE, such as venography, compression ultrasonography, lung scans, or pulmonary angiography. The researchers combined the findings of the studies to see which of the d-dimer tests were most helpful in detecting DVT or PE that was confirmed with standard tests.

What did the researchers find?

Few patients with negative results on d-dimer tests had DVT or PE detected with standard tests. Of the different types of d-dimer tests, the ELISA seemed most useful in ruling out both DVT and PE. Some patients with positive results on d-dimer tests did not have DVT or PE. Moreover, positive results on any type of d-dimer test did not greatly increase the likelihood of DVT or PE.

What were the limitations of the study?

Studies used different standards to detect DVT and PE. Most studies assessed only one d-dimer test and did not compare multiple types of d-dimer tests. Thus, results relating to different types of d-dimer tests were based on indirect comparisons across studies.

What are the implications of the study?

The d-dimer ELISA seems better than other d-dimer tests for excluding DVT and PE.

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